1. Field of the Invention
This invention relates to xerogel and aerogel substrates as sample collection media, and more particularly to a solid phase microextraction device using these substrates.
2. Description of Related Art
Solid Phase Microextraction (SPME) is an analytical chemical isolation technique to extract trace compounds from the air or liquid samples with high efficiency. The extraction device typically uses fused silica (glass) fibers coated with an absorbing polymer (e.g., siloxanes, silanes, silicone). Glass is used to match the thermal expansion of the fiber coating under extreme temperature conditions. The coated glass fiber is capable of extracting organic and organo-metallic compounds from the air and liquid samples. Currently, the coated glass fiber (˜1 cm long) is glued to a metal wire (˜300 μm) supported inside a hollow needle that can be inserted into the hot injection port of a gas chromatograph (GC) or GC mass spectrometer (GC-MS). U.S. Pat. No. 5,691,206 to Pawliszyn describes a method and device for carrying out solid phase microextraction.
This conventional technique is problematic because the glass fiber tip is fragile and can be easily broken off when used in the field or laboratory. The polymer coating has a limited lifetime and can peel away following repeated collections and analyses under the high thermal cycle stress at the GC injection port or after exposure to high field radiation. The manufacturing of the SPME assembly also requires the time-consuming process of gluing the glass fiber to the wire support. The engineering difficulties encountered in the current glass fiber design result in a high cost per unit.
Another disadvantage of the current SPME techniques is the time required extracting the sample by the coated fibers. U.S. Pat. No. 5,693,228 to Koehler et al. provides a device that vibrates the fiber during extraction to shorten adsorption time. However, this approach requires additional hardware incorporated into the conventional SPME syringe.
A need exists for an improved SPME assembly that addresses the deficiencies of the prior art. The present invention circumvents the above-mentioned problems and provides a more robust, highly selective, rapidly adsorbing SPME assembly that effectively extracts samples from gas or liquid samples.